In general, a vehicle-mounted antenna uses conductive material as its base. The material is used as the ground of the antenna, and the material is fixed to a vehicle roof or the like to secure the earth for a vehicle body. In order to make a portion between the conductive base and the vehicle's antenna mounting surface waterproof, a flexible base pad that is made of resin is provided in such a way as to cover an antenna mounting surface-side surface of the conductive base and be fitted onto the conductive base.
In recent years, the weight of such vehicles as electric vehicles and hybrid cars has been reduced in view of fuel economy. The weight of vehicle-mounted antennas is also required to be reduced, and development of a vehicle-mounted antenna with a resin base is underway instead of the vehicle-mounted antenna with the conductive base. For example, Patent Document 1 discloses an antenna base that is made by combining a resin base and a conductive base. On a lower surface of the resin base, around a boss portion, an annular groove is provided, and a ring-shaped seal is fitted. Moreover, a string-like gap cover having a groove portion is wound around a peripheral side surface of the resin base, and the peripheral side surface of the resin base is fitted into the groove portion of the gap cover.